This invention relates to nucleic acid and amino acid sequences of a human lysophosphatidic acid acyltransferase and to the use of these sequences in the diagnosis, treatment, and prevention of cancer and autoimmune disorders.
Lysophosphatidic acid acyltransferase (LPAAT) catalyzes the acylation of lysophosphatidic acid (LPA) to phosphatidic acid. LPA is the simplest glycerophospholipid, consisting of a glycerol molecule, a phosphate group, and a mono-saturated fatty acyl chain. LPAAT adds a second fatty acyl chain to LPA, producing phosphatidic acid (PA). PA is the precursor molecule for diacylglycerols, which are necessary for the production of phospholipids, and for triacylglycerols, which are essential biological fuel molecules.
In addition to being a crucial precursor molecule in biosynthetic reactions, LPA has recently been added to the list of intercellular lipid messenger molecules. LPA interacts with G protein-coupled receptors, coupling to various independent effector pathways including inhibition of adenylate cyclase, stimulation of phospholipase C, activation of MAP kinases, and activation of the small GTP-binding proteins Ras and Rho. (Moolenaar, W. H. (1995) J. Biol. Chem 28-:12949-12952.) The physiological effects of LPA have not been fully characterized yet, but they include promoting growth and invasion tumor cells. Addition of LPA to ovarian or breast cancer cell lines induced cell proliferation, increased intracellular calcium levels, and activated MAP kinase. (Xu, Y et al. (1995) Biochem. J. 309:933-940.) In addition, LPA induced MM1 tumor cells to invade cultured mesothelial cell monolayers. (Imamura, F. et al. (1993) Biochem. Biophys. Res. Comm. 193:497-503.)
Phosphatidic acid (PA), the product of LPAAT, is also a messenger molecule. PA is a key messenger in a common signaling pathway activated by proinflammatory mediators such as interleukin-1xcex2, tumor necrosis factor xcex1, platelet activating factor, and lipid A. (Bursten, S. L. et al. (1992) Am. J. Physiol. 262:C328-C338; Bursten S. L. et al. (1991) J. Biol. Chem. 255:20732-20743; Kester, M. (1993) J. Cell Physiol. 156:317-325.) For example, in a mouse model of inflammatory response, inhibition of LPAAT reduced lipopolysaccharide-mediated endotoxic shock. (Abraham, E. et al. (1995) J. Exp. Med. 181:569-575; Rice, G. C. et al. (1994) Proc. Natl. Acad. Sci. USA 91:3857-3861.) Thus, LPAAT activity may mediate inflammatory responses to various proinflammatory agents.
The discovery of a new human lysophosphatidic acid acyltransferase and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, treatment, and prevention of cancer and autoimmune disorders.
The invention is based on the discovery of a new human lysophosphatidic acid acyltransferase (HLPAAT), the polynucleotides encoding HLPAAT, and the use of these compositions for the diagnosis, treatment, or prevention of cancer and autoimmune disorders.
The invention features a substantially purified polypeptide comprising the amino acids sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1.
The invention further provides a substantially purified variant having at least 90% amino acid sequence identity to the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1. The invention also provides an isolated and purified polynucleotide encoding the polypeptide comprising the sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1. The invention also includes an isolated and purified polynucleotide variant having at least 90% polynucleotide sequence identity to the polynucleotide encoding the polypeptide comprising the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1.
The invention further provides an isolated and purified polynucleotide which hybridizes under stringent conditions to the polynucleotide encoding the polypeptide comprising the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1, as well as an isolated and purified polynucleotide which is complementary to the polynucleotide encoding the polypeptide comprising the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1.
The invention also provides an isolated and purified polynucleotide comprising the polynucleotide sequence of SEQ ID NO:2 or a fragment of SEQ ID NO:2, and an isolated and purified polynucleotide variant having at least 90% polynucleotide sequence identity to the polynucleotide comprising the polynucleotide sequence of SEQ ID NO:2 or a fragment of SEQ ID NO:2. The invention also provides an isolated and purified polynucleotide having a sequence complementary to the polynucleotide comprising the polynucleotide sequence of SEQ ID NO:2 or a fragment of SEQ ID NO:2.
The invention further provides an expression vector containing at least a fragment of the polynucleotide encoding the polypeptide comprising the sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1. In another aspect, the expression vector is contained within a host cell.
The invention also provides a method for producing a polypeptide comprising the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1, the method comprising the steps of: (a) culturing the host cell containing an expression vector containing at least a fragment of a polynucleotide encoding the polypeptide comprising the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1 under conditions suitable for the expression of the polypeptide; and (b) recovering the polypeptide from the host cell culture.
The invention also provides a pharmaceutical composition comprising a substantially purified polypeptide having the sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1 in conjunction with a suitable pharmaceutical carrier.
The invention further includes a purified antibody which binds to a polypeptide comprising the sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1, as well as a purified agonist and a purified antagonist of the polypeptide.
The invention also provides a method for treating or preventing a cancer, the method comprising administering to a subject in need of such treatment an effective amount of a pharmaceutical composition comprising substantially purified polypeptide having the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1.
The invention also provides a method for treating or preventing an autoimmune disorder, the method comprising administering to a subject in need of such treatment an effective amount of an antagonist of the polypeptide having the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1.
The invention also provides a method for detecting a polynucleotide encoding a polypeptide comprising the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1 in a biological sample containing nucleic acids, the method comprising the steps of: (a) hybridizing the complement of the polynucleotide encoding the polypeptide comprising the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1 to at least one of the nucleic acids of the biological sample, thereby forming a hybridization complex; and (b) detecting the hybridization complex, wherein the presence of the hybridization complex correlates with the presence of a polynucleotide encoding the polypeptide comprising the amino acid sequence of SEQ ID NO:1 or a fragment of SEQ ID NO:1 in the biological sample. In one aspect, the nucleic acids of the biological sample are amplified by the polymerase chain reaction prior to the hybridizing step.